Non-chloride admixtures

Mailvaganam, N.P., Bhagrath, R.S. and Shaw, K.L. (1983). Effects of Chloride and Non-chloride Admixtures on Superplasticized Silica Eume Concrete, Annual Meeting of the Transportation Research Board, Washington, D.C. 

The best non-chloride admixture to date appears to be calcium nitrite marketed as a 20% solids solution, it can be readily added to the mix using the usual dispensers. The admixture has therefore been more readily accepted by the ready-mixed concrete industry than the formate-based admixture. Strength development effects produced in concrete are reported to be comparable to those obtained with calcium chloride [40], Table 7.12 shows a comparison of the results for concrete containing calcium chloride, calcium nitrite, and no admixture. In addition to the improvements in both compressive and tensile strengths, calcium nitrite is an effective inhibitor of chloride-induced corrosion. The material is now finding wide acceptance in bridge and parking deck repair. Other non-chloride accelerators used in Russia and special applications include the alkali-metal carbonates (Na CO, K CO, LiCO ). 

The main non-chloride, non-corrosive accelerating admixtures available on the market are of two types (1) accelerating admixtures which accelerate hydration but do not depress the freezing point of water and (2) accelerating admixtures for use in sub-freezing ambient temperatures which depress the freezing point of water. The former contain salts of formates, nitrates and nitrites and are effective for set acceleration and strength development. However, their effectiveness is dependent on the ambient temperature at the time of placement. 

One of the more widely used non-chloride accelerator in North America, the sodium thiocyanate-based multicomponent cold-weather admixture (CWA), is reported to be effective at sub-freezing temperatures, specifically, at ambient temperatures as low as -7°C (20°F) [110]. Data from laboratory studies [110] indicate that the temperature for ice formation in synthetic pore... 

Fig. 7.39 Effect of cement content and a non-chloride accelerating admixture (NCAA) on initial time of set, at concrete and ambient temperatures of 10 C (Nmai [117]).

Cold-weather concrete mixtures incorporating non-chloride antifreeze accelerating admixtures have been used in a number of projects. Two of these projects are profiled. All the concrete mixtures described below were treated with the sodium-thiocyanate-based CWA mentioned earlier. These projects illustrate the impact of this admixture on normal concrete mixtures containing Class C fly ash, since fly ash typically delays time of setting and, hence, would not be a logical choice for cold-weather concrete. 

Calcium formate, of formula Ca(HCOO)2, is a by-product in the manufacture of polyhydric alcohol, pentaerthritol. It is a powder and has a solubility of about 15% in water at room temperature. It is a non-chloride chemical that is used in practice. Many non-chloride accelerating admixture formulations contain formates. Calcium formate is an accelerator for the hydration of C3S at equal concentration, however, CaCl2 is more effective (Fig. 

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